The present invention relates to labyrinth seals and, more particularly, to labyrinth seals in gas turbine engines extending between two co-rotating or counterrotating components.
In gas turbine engines, it is frequently necessary to isolate a given volume, which is defined by one or more rotating parts, in order to confine a fluid within that volume or to prevent a fluid from flowing into that volume. For example, in a gas turbine engine, it is necessary to confine the liquid lubricant used for the shaft bearings to a volume immediately surrounding to the bearings, and at the same time to prevent excessive amounts of cooling air to flow into that volume of lubricating liquid.
Due to the high temperatures and relatively high rotational speeds of the components, often exceeding thousands of revolutions per minute, conventional contacting seals between relatively rotating components are inappropriate. Consequently, labyrinth seals, which comprise a plurality of spaced, radially-projecting seal teeth are used between two relatively rotating parts. Typically, the teeth are mounted on or are integral with one part and project toward the adjacent part with which the seal is to be formed, but do not contact that adjacent part to minimize friction and abrasion. An example of such a labyrinth seal is shown in Malott U.S. Pat. No. 4,463,956, which shows a labyrinth seal mounted on an outer, nonrotating component and extending radially inwardly toward a power transmitting shaft.
A particular problem exists when it becomes necessary to position a labyrinth seal between two corotating or counterrotating components, typically two concentric power-transmitting shafts within a turbine engine. Conventional practice dictates mounting the seal teeth on the inner shaft, since it is easier to machine seal teeth on a shaft outer diameter rather than on a shaft inner diameter. However, as a result of centripetal forces between the fluid isolated by the labyrinth seal and the contacting surface of the seal, the fluid is directed radially outwardly as well, where it passes through the gaps between the outer ends of the seal teeth and the adjacent rotating part, thereby reducing the efficiency of the seal.
Another disadvantage with known labyrinth seals is that the seal teeth have a relatively high susceptibility to stress cracking. Such stress cracks readily propagate to the component on which the teeth are formed, which can result in catastrophic failure of the component and require costly repair.
Accordingly, there is a need for a labyrinth seal designed for use between two co-rotating or counterrotating components in a gas turbine engine which does not transmit stress cracks to the component on which it is mounted and which effects a highly efficient seal.